1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image using a developer.
2. Description of the Related Art
In an image forming apparatus that forms an image using, e.g. a developer including a toner, an electrostatic latent image is formed on a photosensitive drum that serves as an image carrying body. The electrostatic latent image is developed by a developer unit, and a developed toner image is transferred to paper by a transfer unit. The transferred toner image is fixed on the paper by a fuser.
There is known an image forming apparatus of this kind, wherein toner, which remains on the photoconductive drum after the toner image is transferred to the paper, is removed and recovered by a cleaning device. The recovered toner (hereinafter referred to as “recycle toner”) is reused.
For example, a toner recycle mechanism is known. According to this mechanism, recycle toner, which is conveyed by a recovery mixer that is provided in a cleaning device, is directly brought back into the developer unit by a coupling mixer that is provided between the cleaning device and the developer unit.
In this case, the recovered toner is always supplied to the developer unit while the recovery mixer and the coupling mixer are being rotated.
As regards the recycle toner to be reused, there are problems: external additive that is inherently provided on toner particles is partly removed, external additive that is removed from other toner particles may adhere to recycle toner, or paper dust is mixed in recycle toner. Compared to fresh toner, the amount of external additive of which is properly set, an initial rise in charge amount of the recycle toner is not good. If frictional charge that is provided by stirring is deficient, toner that is not charged may be fed to the photosensitive drum.
If the non-charged toner is transferred to paper via the photosensitive drum, such problems as fogging of image or dispersion of toner would occur.